In the field of graphic arts, an image formation system that provides a super-high contrast, particularly, a gamma of 10 or more is required in order to achieve satisfactory reproduction of a continuous tone image by dot formation or a line image.
For this purpose, a special developer called lith developer has conventionally been employed. A lith developer comprises hydroquinone as a sole developing agent and contains, as a preservative, a sulfite in the form of an adduct with formaldehyde having an extremely reduced free sulfite ion concentration, usually 0.1 mol/l or less, so as not to hinder infectious developability. The lith developer has the serious disadvantage that it does not withstand storage for more than 3 days because of its great susceptibility to aid oxidation.
Methods for obtaining high contrast characteristics with a stable developer include a method of using hydrazine derivatives as disclosed in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857 and 4,243,739. According to this method, photographic characteristics of super-high contrast and high sensitivity can be obtained. In addition, since a sulfite can be added to a developer in high concentrations, the developer shows greatly improved stability against air oxidation when compared with the lith developer.
On the other hand, silver halide photographic materials have recently been produced with a remarkably increased speed in coating, drying and finishing steps as compared with conventional production processes. There is a tendency for these materials to be handled under severe conditions with developments in miniaturization of cameras, automatic carrying systems and the like. Accordingly, prevention of fog of silver halide emulsions which is induced by pressure is increasingly important.
Although the above-described high-contrast light-sensitive systems using hydrazine derivatives achieve remarkably increased sensitivity and contrast, the materials used are particularly sensitive to pressure causing scratch fog, especially pressure marks, resulting in significant impairment in photographic quality.
While great efforts have been made to overcome the problem of scratch fog, such as, for example, increasing the film thickness of a protective layer, such a process involves disadvantages such as retardation of development and the like. It has proved difficult to prevent scratch fog while retaining the effects of the above-described hydrazine derivatives in increasing sensitivity and contrast.